Query about my engineering career

You can't apply for B.Tech unless otherwise, you complete your basic qualification that is +2 or Intermediate. If there are any subjects you failed, first of all, you should apply for the supplementary examination and complete the subjects and get the pass certificate in the exam. After that the next year when the notification comes for entrance test you have to apply for that and get qualified with a good rank. Then only you can join in B.Tech. Otherwise, you can't be allowed to join in B.Tech. As of now, your first task is to clear your intermediate or +2.

Engineering admissions usually begin post results as you will be allotted to college as per your score and rank. If you are confident you will clear supplementary exam then consult admission department of BTech about choices. I am sure they will ask you to submit form for now and update the results before some deadline. All the best.